1. Field of the Invention
The present invention relates to a toner for developing latent electrostatic images formed by electrophotography, electrostatic recording method, or electrostatic printing method, to visible toner images.
2. Discussion of Background
Generally, in electrophotography and electrostatic printing, latent electrostatic images formed on an electrostatic image bearing member are developed to visible toner images, using a two-component toner comprising toner particles and carrier particles, or a mono-component toner comprising electrically charged toner particles, which are supplied in the form of a thin layer to the electrostatic image bearing member, using, for instance, a toner supply roller such as a development sleeve with a blade. When necessary, the developed toner images are transferred to a transfer sheet made of, for example, paper, and fixed thereon by the application heat and/or pressure thereto, or with the application of a vapor of a solvent, whereby image-bearing copies are obtained.
Of varieties of image fixing methods, which are suitable for the above-mentioned development methods, currently a heat roller image fixing method is widely used because of the advantages of higher thermal efficiency and higher image fixing speed over other image fixing methods.
When high speed image fixing is performed using the heat roller image fixing method, it is required that a toner for use in the image fixing method have excellent low-temperature image fixing performance, that is, a lower image fixing limit temperature of the toner is required to be significantly low. In order to attain this, if a resin which can be softened at a low temperature is added to the toner as a binder resin, at least part of toner images developed by the toner is apt to adhere to the surface of a heat roller in the course of the image fixing process. If this takes place, the toner which has adhered to the heat roller is then transferred to a copy paper, with the occurrence of the deposition of the toner on the background of the copy paper. Thus, a so-called hot offset phenomenon takes place. Furthermore, when the above-mentioned hot offset phenomenon takes place, the copy paper is apt to be wound around the heat roller. Thus, a so-called paper winding phenomenon is also apt to take place. This paper winding phenomenon is apt to take place particularly when the temperature of the heat roller is low. In the case of a color toner, when the above-mentioned hot offset phenomenon takes place, the glossiness of color images is significantly lowered. In addition, when the above-mentioned resin having a low softening temperature is added to the toner, toner particles thereof are apt to aggregate, and a so-called blocking phenomenon is apt to take place in the course of the transportation of the toner or while the toner is preserved in copying machine. Thus, the preservability of the toner is impaired.
In order to prevent the occurrence of the above-mentioned phenomena, in Japanese Laid-Open Patent Applications Nos. 51-143333, 57-148752, 58-97056 and 60-247250, it has been proposed to add as a releasing agent, solid silicone varnish, higher fatty acid, higher alcohol or wax to the toner. None of these releasing agents, however, exhibit satisfactory anti-hot offset performance and anti-paper-winding performance while maintaining excellent low-temperature image fixing performance.
Specifically, conventional polyolefin waxes such as low-molecular-weight polyethylene and polypropylene exhibit effective anti-hot-offset phenomenon but do not impart sufficient low-temperature image fixing performance to the toner for use in practice.
Vegetable waxes such as carnauba wax and candelilla wax exhibit effective anti-hot-offset phenomenon and low-temperature image fixing performance, but do not exhibit sufficient anti-paper-winding performance for use in practice. Solid silicone varnish, solid silicone oil, amide wax, higher fatty acid, higher alcohol and montan wax exhibit effective low-temperature image fixing performance, but do not exhibit sufficient anti-hot-offset performance and anti-paper-winding performance. Moreover, the use of such conventional releasing agents often causes a toner-filming phenomenon or a toner-spent phenomenon, in which the releasing agent is separated from the toner and adheres to the photoconductor and the surface of carrier particles for the toner. When such a phenomenon takes place, it is difficult to form high quality images continuously for an extended period of time.
In an attempt to lower the image-fixing temperature and to impart to the toner excellent anti-hot-offset performance and the anti-blocking performance, the following various proposals have been made by specifying the composition, thermal properties and molecular weight distribution of a binder resin for use in the toner:
For example, Japanese Laid-Open Patent Application 3-139663 proposes to specify a binder resin with a softening temperature thereof; Japanese Laid-Open Patent Application 3-152558 proposes to specify a binder resin with a molecular weight distribution thereof: Japanese Laid-Open Patent Application 3-145654 proposes to specify a cross linking agent for use in a binder resin; Japanese Laid-Open Patent Application 3-206465 proposes to specify the production of a binder resin using a block polymer; Japanese Laid-Open Patent Application 3-219262 proposes to specify a binder resin with the viscoelastic properties thereof; Japanese Laid-Open Patent Application 3-188468 proposes to specify a binder resin with an acid value/a hydroxyl group value thereof; Japanese Laid-Open Patent Applications 3-203748 and 3-229264 propose to specify a polyester with an acid value thereof; Japanese Laid-Open Patent Applications 3-231757, 4-353866 and 5-100477 propose to specify binder resins with the viscoelastic properties thereof; Japanese Laid-Open Patent Applications Nos. 4-20512, 4-23816, 4-23817 and 4-50216 propose to specify a binder resin as a styrene-acrylic block copolymer; Japanese Laid-Open Patent Applications Nos. 4-26858, 4-81769 and 4-81770 propose to specify a binder resin as a block or graft copolymer of a crystalline polyester and a vinyl copolymer; Japanese Laid-Open Applications 4-81863 and 6-348058 propose to specify a binder resin with a peak of a molecular weight thereof; Japanese Laid-Open Application 4-190242 proposes to specify a toner with a molecular weight distribution of a binder resin and an image fixing method for use with the toner; Japanese Laid-Open Application 4-254863 proposes to specify binder resins as a polyester and a styrene/acrylic polymer with particular molecular weights thereof; Japanese Laid-Open Patent Applications 4-264559, 4-264560, 4-274253, 5-19531 and 5-188638 propose to specify a binder resin with a molecular weight distribution thereof; Japanese Laid-Open Patent Application 4-277755 proposes to specify a binder resin as a particular block copolymer; and Japanese Laid-Open Patent Application 4-309962 proposes to specify a binder resin by the use of an ionomer.
The above-proposed binder resins, however, are not satisfactory.
Japanese Laid-Open Patent Application 60-31146 proposes a photodegradation capsuled toner; Japanese Laid-Open Patent Application 62-148969 proposes a toner using an exothermic amplification material; Japanese Laid-Open Patent Application 63-281168 proposes a capsuled toner having a thermotropic liquid crystal polymeric shell; Japanese Laid-Open Patent Application 1-149062 proposes a capsuled toner of which volume can be expanded when exposed to light; Japanese Laid-Open Patent Application 2-251971 proposes a toner using a cross-linking thermotropic liquid crystal polymer; Japanese Laid-Open Patent Application 3-118550 proposes a toner comprising an exothermic material; Japanese Laid-Open Patent Application 4-250460 proposes a toner comprising an cyclohexanone derivative; Japanese Laid-Open Patent Application 4-291355 proposes a toner comprising a Bisphenol F-type epoxy resin; Japanese Laid-Open Patent Application 4-329551 proposes a toner comprising a near infrared absorption pigment and an ethylenic unsaturated compound which is cured when exposed to near infrared rays; Japanese Laid-Open Patent Application 4-100475 and Japanese Laid-Open Patent Application 4-100476 propose a toner comprising a heat decomposable resin using an azo polymerization initiator; Japanese Laid-Open Patent Application 5-173364 proposes a toner comprising a cyclohexanone-based ketone resin; Japanese Laid-Open Patent Application 8-15894 proposes a toner prepared using a polymer with an acid value or a hydroxyl group value of 1 or more, with the deposition of a metal alkoxide on the surface of the toner; and Japanese Laid-Open Patent Application 8-15902 proposes a capsuled toner prepared by using a chlorine-containing monomer in the capsule thereof.
The above-proposed toners, however, are not satisfactory for use in practice.
The inventor of the present invention proposed the use of a star polymer as a binder resin for a toner in Japanese Laid-Open Patent Application 7-261457. However, the resolution of images obtained by the toner is not satisfactory. Furthermore, the star polymer used as the binder resin basically has charging properties, but the charging performance thereof is not stable enough with time and not satisfactory for use in practice.